In World War Two, the British counted the bullet holes in airplanes that returned from missions. Based on where the holes were, they now knew where not to bother putting armour on their airplanes (see this Mother Jones Article).
Documentation seems to be a bit like this; one of my Phrankism is: Documentation is a complete and utter waste of time… until the moment when you need it. Therefore figure out when you will need the documentation and work backwards from there.
The challenge when creating documentation is what is needed and what will never be read (e.g. the bullet holes in the returning airplanes). In the old days, one way to do this was to look at pages in a binder and see which ones were the dirtiest, dogged eared and marked up. The pristine pages were never read and the beat up ones were the important pages.
Binders have largely gone the way of the DC-3s and have been replaced with digital mediums such as Wikis. Over the past seven years I have been using Wiki as the primary documentation ‘container’. One of the benefits of using such an electronic container is the ability to measure when a page was created and its modifications. Tools such as SharePoint also allows you to track how often a page was visited. Ideally a rating tool (such as what Microsoft uses for its help pages) measures both quantitative and qualitative values (e.g. how helpful was the page to you).
The result for organizations? Focus documentation efforts on the pages never updated, opened or rated. Ask if a page is digitally pristine, is it needed? Is the organizational knowledge being documented so obvious that it need not be written down? Is the page so poorly written that the organization avoids or ignores it?
One last little trick on documentation is to ensure that each page is assigned an owner. Ask them during performance review time why the page was never read, is it needed or how to improve it.
Documentation is a complete waste of time. The best way to improve the value of the effort is to ensure the pages in the binder or in the wiki come back shot up, bruised, battered and successfully used in the war of Organizational Knowledge and Productivity.